Field of the Invention
The present invention relates to a water-based ink for ink-jet recording, and an ink container which accommodates therein the water-based ink for ink-jet recording.
Description of the Related Art
In a water-based ink for ink-jet recording (hereinafter referred to also as a “water-based ink” or an “ink” in some cases), a pigment is widely used as a colorant. In the water-based ink using the pigment, however, the particles of the pigment often sediment (settle) as time passes. The sedimentation of the pigment particles causes a problem(s) such as the increase in the viscosity of the water-based ink in the vicinity of nozzles of an ink-jet head, any unsatisfactory jetting (discharge), any non-uniform density in the water-based ink, etc.
As a solution to the above-described problem(s), there is proposed a self-dispersible dye-pigment containing a pigment, a polymer covalently bonded to the pigment, a dye bonded to the polymer, and a dispersant covalently bonded to at least one of the pigment, the polymer and the dye (see, for example, Japanese Patent Application Laid-open No. 2006-176756 corresponding to U.S. Patent Application Publication Nos. US2006/0089421 and US2006/0089422).
In the above-described self-dispersible dye-pigment, however, it is necessary to use the different kinds of the colorant that are the pigment and the dye. Further, in the water-based ink, a pigment having a large mean particle diameter is used in some cases for the purpose of obtaining a high optical density (OD value), the problem of the sedimentation of pigment particles is particularly conspicuous in such a case of using the pigment having the large mean particle diameter. Accordingly, any new method for addressing the pigment sedimentation is required, in view of the stability, etc., of the water-based ink. Further, regarding a water-based ink in which the pigment sedimentation is suppressed, there is a demand for a new water-based ink for ink-jet recording which has excellent weatherability (weather resistance) and in which the extent of change in color is small (color is less likely to change or hardly changes) over time.
In view of the above-described situation, an object of the present teaching is to provide a water-based ink for ink-jet recording which is capable of suppressing the sedimentation of a self-dispersible black pigment, in which a high optical density (OD value) is obtainable, which has excellent weatherability and in which color hardly changed or color changes only to a small extent over time.